The present invention relates to the key top of a press button switch mounted on a variety of electronic devices, such as communication devices, which include cellular phones and automobile phones, and audio devices.
In the prior art, it is desired that electronic devices including mobile communication terminals, such as a cellular phone or an automobile phone, be light and compact. Accordingly, it is desirable that press button switches used in such electronic devices also be light, compact, and thin. To satisfy such desires, a key top is used in the art having a translucent body and a translucent resin film adhered to all the surfaces of the body, except for the rear surface. Such a key top is widely used nowadays.
FIG. 6 is a cross sectional view of a prior art key top. The key top comprises a key top body 32 made of a translucent resin and a translucent resin film 31 adhered to the outer surface of the key top body 32, except for the rear surface 32a. This forms a press button 35, which projects frontward from the resin film 31 of the key top. Further, a graphical symbol layer 33 is arranged between the film 31 and the body 32, which form the press button 35, to display a graphical symbol, such as a character, on the press button 35. The film 31 is typically shaped corresponding to a profile of the key top body 32. Then, resin is injected into the shaped film 31 to manufacture the key top. Therefore, the rear surface 32a of the key top body 32 has a gate mark 34 at a position corresponding to a gate, through which resin is injected when injection molding the body 32.
In recent years, the variety of designs for such a key top has increased drastically. For example, press buttons used in cellular phones have a wide variety of designs. Under such circumstances, such a key top is required to be designed with high quality and superior visibility of the graphical symbol on the front surface of the key top.
Currently, however, the key top has the gate mark 34 on the rear surface of the key top body 32. Therefore, the gate mark 34 is visible through the film 31 and the key top body 32 when viewing the key top body 32 from the front of the press button 35. This affects the appearance of the current key top in an undesirable manner. The gate mark 34 may distort the image of the graphical symbol layer 33 formed on the rear surface of the resin film 31 when viewing the graphical symbol from the front of the press button 35. That is, the gate mark 34 impairs the visibility of the graphical symbol layer 33, which provides the graphical symbol to the press button 35 of the key top. This reduces the aesthetic appeal of the key top.
To solve this problem, the gate mark 34 may be arranged in a peripheral portion of the key top body 32 at a position where the gate mark 34 does not oppose the graphical symbol layer 33, as shown by broken lines in FIG. 6. However, in this layout, the gate mark 34 is still visible from the front of the press button through the key top body 32. Thus, such a layout does not solve the above problem.
Referring to FIG. 7, Japanese Laid-Open Patent Publication No. 8-7698 discloses a key top body 32 having a rear surface projected further rearward from the rearmost surface of a resin film 31. The key top body 32 also has an extending portion 36 extending outward from the outer periphery of the projected portion of the key top body 32. A gate mark 34 is formed on the extending portion 36.
The above key top is formed by performing injection molding. The material of the key top body 32 is injected into a recess formed in the film with the desired shape. When molten resin is injected into the cavity of a mold through a gate, the air remaining in the cavity prevents the cavity from being completely filled with the molten resin in a uniform manner. This causes the outer surface of the molded key top boy 32 to become uneven and unsmooth. As a result, the aesthetic appeal of the key top is reduced.
The present invention is directed to deal with the drawbacks abovementioned.
In one aspect of the present invention, a key top comprises a resin film having a front surface and a rear surface; a key top body made of resin, said key top body having a rear surface and a peripheral surface, said key top body being covered by the resin film except for the rear surface thereof; and a first extending portion having a rear surface and extending outward from the peripheral surface of the key top body. The first extending portion includes a gate mark formed by the mold gate and a vent mark formed by the mold vent when molding the key top body, which are located on the rear surface of the first extending portion. The rear surface of the key top body and the rear surface of the first extending portion are flat and extend along a plane located rearward from the rear surface of the resin film.
In another aspect of the present invention, a mold for forming a key top by injecting resin therein is provided. The mold comprises (a) an upper mold section including a first cavity formed in the upper mold section, the first cavity having a rim from which a step-out recess extends, surrounding the first cavity, and the step-put recess having a depth less than that of the first cavity; and (b) a lower mold section adapted to mate with the upper mold section, the lower mold section including a second cavity formed in the lower mold section, the second cavity having an area that opposes the step-out recess when the mold sections mate together. Said area includes a gate for injecting resin into the cavities when the mold sections mate together, and a vent for venting gas from the cavities as resin is injected.
In still another aspect of the invention, a method of forming a key top is provided. The method comprises (a) injecting resin in non-solid form into a mold to form a key top body with the key top body including an outwardly extending portion, from where the resin is injected and from which gas is vented, and the resin being translucent when solidified; (b) solidifying the resin; (c) forming a graphic symbol on a translucent resin film; and (d) fusing the translucent resin film to the upper surface of the key top body. The graphic symbol is surrounded by the extending portion from a plan view of the key top body.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.